linux-kernel - Re: [PATCH v6 6/6] drm/drm-file: Show finer-grained BO sizes in drm_show_memory

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Date:   Wed, 20 Sep 2023 16:32:46 +0100
From:   Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
To:     Adrián Larumbe <adrian.larumbe@...labora.com>,
        maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        tzimmermann@...e.de, airlied@...il.com, daniel@...ll.ch,
        robdclark@...il.com, quic_abhinavk@...cinc.com,
        dmitry.baryshkov@...aro.org, sean@...rly.run,
        marijn.suijten@...ainline.org, robh@...nel.org,
        steven.price@....com
Cc:     linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, healych@...zon.com,
        Boris Brezillon <boris.brezillon@...labora.com>,
        kernel@...labora.com, freedreno@...ts.freedesktop.org
Subject: Re: [PATCH v6 6/6] drm/drm-file: Show finer-grained BO sizes in
 drm_show_memory_stats


On 20/09/2023 00:34, Adrián Larumbe wrote:
> The current implementation will try to pick the highest available size
> display unit as soon as the BO size exceeds that of the previous
> multiplier. That can lead to loss of precision in contexts of low memory
> usage.
> 
> The new selection criteria try to preserve precision, whilst also
> increasing the display unit selection threshold to render more accurate
> values.
> 
> Signed-off-by: Adrián Larumbe <adrian.larumbe@...labora.com>
> Reviewed-by: Boris Brezillon <boris.brezillon@...labora.com>
> Reviewed-by: Steven Price <steven.price@....com>
> ---
>   drivers/gpu/drm/drm_file.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
> index 762965e3d503..34cfa128ffe5 100644
> --- a/drivers/gpu/drm/drm_file.c
> +++ b/drivers/gpu/drm/drm_file.c
> @@ -872,6 +872,8 @@ void drm_send_event(struct drm_device *dev, struct drm_pending_event *e)
>   }
>   EXPORT_SYMBOL(drm_send_event);
>   
> +#define UPPER_UNIT_THRESHOLD 100
> +
>   static void print_size(struct drm_printer *p, const char *stat,
>   		       const char *region, u64 sz)
>   {
> @@ -879,7 +881,8 @@ static void print_size(struct drm_printer *p, const char *stat,
>   	unsigned u;
>   
>   	for (u = 0; u < ARRAY_SIZE(units) - 1; u++) {
> -		if (sz < SZ_1K)
> +		if ((sz & (SZ_1K - 1)) &&

IS_ALIGNED worth it at all?

> +		    sz < UPPER_UNIT_THRESHOLD * SZ_1K)
>   			break;

Excuse me for a late comment (I was away). I did not get what what is 
special about a ~10% threshold? Sounds to me just going with the lower 
unit, when size is not aligned to the higher one, would be better than 
sometimes precision-sometimes-not.

Regards,

Tvrtko

>   		sz = div_u64(sz, SZ_1K);
>   	}